DE69534033T2 - Element with a coating of solid lubricant for a rolling bearing with grease lubrication - Google Patents

Description

The The present invention relates to a lubricated rolling bearing, in which parts of the bearing, such as the bearing cage or roller ends, with a solid lubricant coating are coated.

roller bearing generally include an outer and an inner ring, rolling elements in the bearing space between the rings and a cage around the rolling elements to keep in a predetermined mutual distance, as well a lubricant to use for To provide lubrication.

In spite of The presence of the lubricant is the cage and the rolling elements while the operation of such a bearing in sliding contact. This results Friction and wear, which limit the service life of such sliding contact.

document GB 826 091 A describes cages with a metallic body coated with a thin plastic layer, such as polyamide or polytetrafluoroethylene containing about 3% MoS ₂ or graphite.

Around the friction and the wear too Reduce, it is known, a manganese phosphate coating in the cage pockets to apply the rolling elements contain. Such a manganese phosphate coating is, however, out different reasons not satisfactory. One reason is that these coatings only for the "start up" of the warehouse are useful, i.e. only an initial one Provide friction reduction at the beginning of service life. After a certain period of time, the phosphate coating disappears, causing a metal-to-metal contact, a higher running temperature and / or the aging of the lubricant which is introduced in the bearing, caused. In some cases This can be done locally to "burned" lubricant and / or Run dry storage of the bearing. Therefore, some lubricant lubricated bearings have ordinary Manganese phosphate coated steel cages reduced tribological Protection on the contacts between roller and cage pocket. This generally leads to form brown stripes on rollers and races. This is attributed to high sliding contact load and poor lubrication conditions between Roller and bearing contacts.

Other Factors indicating the condition of the lubricant in the bearing, the running temperature and adversely affect the useful life of the bearing, are the high heat load, which occurs between the bearing ring and the rolling elements and the Lack of lubricant supply between the components of the Camp.

When As a result of these problems, bearings should be phosphate-coated cages include, often be relubricated; if such frequent lubrication fails, the useful life of the bearing is reduced.

task The invention therefore is to provide a rolling bearing, which does not have the above-mentioned disadvantages. The task is thereby solved, that the bearing cage with a coating to reduce the running temperature of the cage and thus the bearing is coated.

The invention therefore relates to a bearing cage for a rolling bearing, wherein the cage is coated with a lubricant-containing coating for reducing the running temperature of the cage, the coating containing a disulfide or diselenide of a Group V or VI transition metal. According to a particularly preferred embodiment, the coating contains MoS ₂ and / or WS ₂ , optionally in combination with polytetrafluoroethylene (PTFE).

A number of rolling bearings with MoS ₂ coatings on the cage and / or as a solid lubricant are known in the art, see eg US-A 3,500,525, JP-A-62 141 314 and JP-A-3 255 223. However, these documents all refer to bearings for use in (high) vacuum and / or at elevated temperatures (250 ° C or higher) which, for obvious reasons, do not permit lubrication of lubricant. Such non-lubricant lubricated bearings for use in a high vacuum / temperature environment are not claimed by the present application.

The description of the British patent GB 1 515 643 A describes ball and roller bearings in which the balls and rollers are held in place by a cage, the cage having a cover layer of low friction plastic material, such as PTFE, to reduce contact friction.

However, this reference is silent with respect to solid lubricant-containing coatings such as coatings containing MoS ₂ and / or WS ₂ . As shown by the examples below, the presence of such a coating, such as a coating containing MoS ₂ / PTFE, on the bearing cage has a beneficial effect on the properties of the lubricant in the bearing as compared to a coating containing only PTFE.

Even though not limited to It is believed that the presence of solid lubricants according to the invention in the polymer coating improved affinity with the Fat / oil and an improvement of the load-bearing properties under bad Lubricating conditions and thereby the life of the Increased lubricant.

Farther It is well known in the art that the rate of wear of PTFE is very bad, so that only a PTFE coated bearing has a relatively short life compared to the solid Lubricant coatings of the present application.

Of the Expression "solid Lubricant "is well-known in the art and can be generally defined be considered a solid material with low friction and less Wear rate. The term "solid Lubricant coating "is hence herein as a coating with good adhesion, containing the solid lubricants contains Are defined.

According to the invention, the solid lubricant comprises a disulfide or diselenide of a transition metal of group V or VI of the Periodic Table of the Elements and / or a combination thereof. Particularly preferred solid lubricants are MoS ₂ and WS ₂ . Such coatings are well known in the art and described, for example, in the references mentioned above.

The solid lubricants according to the invention is preferably in a mixture with an organic Resin such as PTFE, polyamide or other polymeric materials such as polycarboxindole or polypyrrole. These resins serve as a binder to the solid lubricant to carry, resulting in a much better performance of the camp.

Commercially available examples of coatings containing MoS ₂ include the MoS ₂ / PTFE containing coating manufactured by Eeonyx-Company, USA, the PTFE / MoS ₂ coating manufactured by Dowty, UK (product 1052), and the MoS ₂ containing Molykote coating 7409 ( Dow Corning).

An example of a commercially available WS ₂ coating is Dichronite.

Such Coatings are well known and appreciated in the art according to the state of the art for Corrosion protection and permanent lubrication of bolts, hinges etc. as well as the lubrication of machine and gear parts, e.g. Piston used.

The present invention on the surprising Realization that while Operating bearings bearing solid lubricant coatings according to the invention coated, still an effective amount of lubricant on their surfaces even if these coated surfaces are lower Show friction as metallic surfaces commonly found in uncoated bearings are present. Because of the lower friction the coating would be had to be expected that the solid lubricant coatings the lubricant would be less effective on the cage.

During the Operation of the bearing should be all elements of the bearing, in sliding contact are on their contact surfaces Have lubricant. In particular, there are e.g. in rolling bearings a constant pressure, which is the lubricant because of the centrifugal force, which acts on the lubricant when the bearing is at high speeds rotated, outward suppressed. Therefore, it was expected that with cages, coated with a solid lubricant coating, the lubricant is pressed from the critical contact surfaces would and / or even completely out of the cage would be ejected and therefore the for the lubrication available Lubricant quantity would be reduced.

However, in accordance with the present invention, it has now been found that the negative effect of the solid lubricant coating of the invention to hold the lubricant in place is more than offset by the lower running temperature obtained when such a solid lubricant coating is used on the cages , For this reason, the solid lubricant coating has a general positive effect on the life of the lubricant, the service life of the bearing and the required lubrication intervals.

In this regard, coatings containing the solid lubricants in a plastic material, such as PTFE, give better results than coatings containing only PTFE, as described in the specification of patent GB-1 515 643. Because of their higher surface tension, the λ / MoS ₂ coatings provide better "wetting" of the surfaces of the cage with the oil and / or grease, better grease / oil compatibility and adhesion, and an increase in load-bearing properties, with lubricant service life is further improved.

The better adhesion of coatings containing solid lubricant according to this Invention on the coated surfaces is also an important Factor to keep the lubricant in place.

Next achieving a lower running temperature and better adhesion of the Lubricant, these coatings also provide better adhesion on the substrate (e.g., the bearing cage) ready as the phosphate coating and / or PTFE coatings according to the state the technique, so this over a longer Duration are effective.

Another advantage of PTFE / MoS ₂ coatings is that they are less hazardous to the environment than, for example, leaded coatings.

However, the invention is not limited to coatings containing MoS ₂ / PTFE and any solid lubricant coating according to the invention which results in a low running temperature of the cage and / or bearing can be used. Such solid lubricant coatings can be easily determined by a person skilled in the art by the methods described in the example, ie determination of the running temperature of the bearing in a manner known per se. Preferably, the solid lubricant coatings also exhibit good adhesion to the substrate.

According to the present Invention can be the entire cage be coated with the solid lubricant coating or only the parts and surfaces of the cage, which in sliding contact with the rolling elements or Guide rings, like the cage pockets and / or cage bars, stand, as is clear to the person skilled in the art. Coatings of the cage bars with a solid lubricant coating according to the invention can also be used Become smaller, more accurate cage pockets to produce with lower friction.

The Coating according to the invention provides an improvement in cage behavior in ball and roller bearings, what the durability of the camp improved, as can be seen in life tests for bearings. The coating according to the invention may be in the bore of e.g. Vibrating screen bearings (Vibrating Stream Barings, SRB).

The Applying a solid lubricant polymer coating, preferably Containing PTFE sintered with a predetermined thickness of 10-15 microns became what a cage bag with a given pocket play and a given cage bar shape which gives the cage allows an eccentric barrel, provides an ideal connection for improving rolling element guidance. hereby become negative sides, like an increasing cage friction by a wear process, scraping off the lubricant and metal-to-metal contact, strong sounds of the cage and a low life by using a solid lubricant coating according to the invention avoided in this type of application.

According to one preferred embodiment Both the cage pockets as well as the cage bars with a solid lubricant coating according to the invention for reduction the running temperature coated.

• – eine niedrigere Lauftemperatur des Käfigs und des Lagers verglichen mit Manganphosphat-Beschichtungen gemäß dem Stand der Technik;
• – das Schmiermittel um die Kontakte bleibt über einen längeren Zeitraum in gutem Zustand, woraus eine Verbesserung der allgemeinen Schmierung resultiert;
• – örtliches Verbrennen von Schmiermittel tritt nicht auf;
• – eine längere nutzbare Betriebsdauer des Wälzlagers;
• – ein besseres Zurückhalten des Fett/Schmiermittels im Käfig, insbesondere auf den Käfigstangen, die zwischen den Wälzelementen positioniert sind und welche an diesen Elementen gleiten;
• – längere Intervalle zwischen Schmiervorgängen;
• – niedrigere Wärmespannungen hinsichtlich der Wälzelemente;
• – besseres Zurückhalten des Schmiermittels auf den Wälzelementen selbst, was zu einer geringeren oder sogar zu keiner Bildung brauner Streifen auf diesen Elementen und den Ringen führt;
• – die Anwesenheit einer dickeren Schmierstoffschicht auf den Wälzelementen, wobei die Schmierstoffschicht nicht leicht von den Käfigstangen abgekratzt wird, wodurch auch eine bessere Schmierung zwischen den Wälzelementen und den Lagerringen bereitgestellt wird;
• – die beschichteten Oberflächen der Erfindung können mit Nuten versehen sein, um das Schmiermittel an die Kontaktoberflächen zu fördern, was zu einer besseren Schmierung der kritischen Oberflächen während des Betriebs führt.

By coating the cage of a rolling bearing with such a coating, the following advantages are achieved:

• A lower running temperature of the cage and the bearing compared to manganese phosphate coatings according to the prior art;
• The lubricant around the contacts remains in good condition for an extended period of time, resulting in an improvement in general lubrication;
• - local burning of lubricant does not occur;
• - A longer useful life of the rolling bearing;
• A better retention of the grease / lubricant in the cage, in particular on the cage bars, which are positioned between the rolling elements and which slide on these elements;
• - longer intervals between lubrication processes;
• - lower thermal stresses with respect to the rolling elements;
• - Better retention of the lubricant on the rolling elements themselves, resulting in less or even no formation of brown stripes on these elements and the rings;
• The presence of a thicker layer of lubricant on the rolling elements, the lubricant layer not being easily scraped off the cage bars, thereby also providing better lubrication between the rolling elements and the bearing rings;
• The coated surfaces of the invention may be grooved to promote the lubricant to the contact surfaces resulting in better lubrication of the critical surfaces during operation.

During the Operation, the lubricating film by rolling over slowly from the contact path emotional. In non-vibrating, poorly lubricated line contact layers and other types of lubricated bearings, the grooves in the coated surfaces An additional provide active mechanism to replenish the lubricant film distribute, causing a rupture of the lubricant film and subsequent failure of the warehouse. By applying a pattern of grooves on the cage wall leads the Sliding motion between roller and cage bar for a lubricant movement to the center and so enriches the lubricant in the middle of the web on, causing a ripping of the lubricant film and its consequences described above counteracted. By applying the same groove pattern both on the cage bars, occurs the lubricant film transport to the center of the roll path regardless of the direction of the bearing rotation. Therefore, these grooves lead to a Decrease in contact stresses and an increase in life both the lubricant and the bearing. The form and the Number of grooves hanging e.g. from the used cage and bearings and the use of suitable grooves will be apparent to those skilled in the art.

The solid lubricant coatings according to the invention can be applied by any suitable method, such as dipping, spraying, etc., which methods are obvious to a person skilled in the art and / or are described, for example, in the above-mentioned prior art. Preferably, however, the PTFE / MoS ₂ coating is applied by "shot peening", which is disclosed in US patent application Ser US 5,262,241 is described. Cages coated by this method provide even better results than cages that have been coated by spraying or dipping.

Preferably the coating has a thickness of 5-10 μm. It is possible, however, one thicker coating to obtain a cage pocket, the a better leadership of the rolling element allows while they are the solid lubricant according to the invention maintains.

The Use of solid lubricant coatings according to the invention can also the lubrication behavior of the roller flange contact improve the lubrication of tapered roller bearings. This application overcomes the bad lubrication and wear problems of roller flange contacts in the Operation, especially under high applied axial load conditions. Improving the life of the bearing can be done easily can be achieved by applying the coatings on the roll ends. The contact temperature is reduced and the result is minimal metallic wear and tear this will be a longer one Lifespan of the lubricant expected.

The invention therefore further relates to the use of coatings containing MoS ₂ and / or WS ₂ as defined in claim 7.

The invention will now be compared by the following example, in which the behavior of the solid lubricating coating according to the invention for reducing the running temperature with a manganese phosphate coating according to the prior art and a PRCA coating which provides no lower running temperature and a coating containing only PTFE , described. The 1 - 5 are graphs of running temperature versus time for the bearings used in the examples, and show

1 : Storage behavior of standard phosphate cages

2 : Storage Behavior of PCRA Coated Cages (Comparison)

3 : Storage Behavior of Eeonyx-coated Cages (Invention)

4a : Storage Behavior of Dowty Coated Cages (Invention)

4b : Storage Behavior of Molykote-coated Cages (Invention)

5 : Storage behavior of selected coatings on cages

example

1st storage test

Of the Storage test with standard and coated cages was made according to the SKF R2F "A" experimental conditions as shown in Table 1 performed.

Table 1

2. Test materials

Polymer-coated SRB cages based on methyl acrylate and / or fluoropolymer and polytetrafluoroethylene (PTFE) / MoS ₂ were used in this study. For the production of coatings on cages, both proprietary and commercial coating processes based on these materials have been used. Details of the coatings and suppliers are listed in Table 2.

Table 2

• * Vertreter von Dow Corning in den Niederlanden

All test cages used were based on the standard E-design. At the time of the project, simple steel cages, ie untreated cages, could not be obtained; all polymer / anti-friction coated cages were based on pre-phosphated cages. The phosphate coating was used in the Cage Factory (SKF Ball Bearings Industry, Veenendaal, The Netherlands) by rotary end treatment. Table 3 summarizes the test program performed. Table 3

• * Representative of Dow Corning in the Netherlands

3. Behavioral Ranking

All tested bearings were according to their behavior regarding the Running temperature (ΔT) and visual damage inspection classified.

flow temperature

The Storage temperature (outer ring) was continuously monitored and recorded by computer until the end of the trial period.

The The preset temperature limit for ending the test is 200 ° C. The current displayed Bearing temperature, ΔT, is the difference between the outer ring surface temperature and the ambient temperature. The evaluation is generally based insist that low running temperature small losses of solid lubricant guaranteed and a smooth curve usually requires good behavior.

Visual observation

5:

Rollen nahezu wie neu/geringer oder kein Verschleiß an Rollen-Käfigstangen-Kontakten

4:

Rollen mit einigen Kratzern/leichter Verschleiß an Rollen-Käfigstangen-Kontakten

3:

kleine braune oder polierte Streifen (< 30% der Rollenoberfläche)/kleiner Verschleiß an Rollen-Käfigstangen-Kontakten

2:

moderate braune oder polierte Streifen (30–50% der Rollenoberfläche)/mittlerer bis hoher Verschleiß an Rollen-Käfig-Kontakten

1:

große braune/polierte Streifen (> 50% der Rollenoberfläche)/mittlerer bis hoher Verschleiß an Rollen-Käfig-Kontakten

The rolling elements and bearings of all test bearings were examined and ranked according to the following levels. the higher the rating, the better the cage fulfills its tribological function. The ranking was done per camp page.

5:

Rolls almost as new / low or no wear on roller cage bar contacts

4:

Rolls with some scratches / slight wear on roller cage bar contacts

3:

small brown or polished stripes (<30% of roll surface) / small wear on roller cage bar contacts

2:

moderate brown or polished stripes (30-50% of roll surface) / medium to high wear on roll cage contacts

1:

large brown / polished stripes (> 50% of the roll surface) / medium to high wear on roller cage contacts

4. Test results

a. Behavior of standard manganese phosphate-coated cages (State of the art)

Three bearings with standard phosphate-coated cages were tested. The for all attempts (see 1 High temperature peaks observed indicate problems of bearing lubrication under experimental conditions. The duration of all observed temperature spikes is relatively short and the subsequent drop may be due to lubricant supplementation. It is obvious that the rapid increase in temperature is mainly due to the high friction losses between roller and cage pocket contacts. It has been observed that the mean running temperature, ΔT, is in the range of 45-50 ° C (cf. 1 ) lies.

visual Controls of the experimental camps (Nos. 2, 4 & 10) were performed. The Ranking is shown in Table 4. The classification with 3 and lower shows the formation of brown stripes on rolls and Raceways. The phosphate coating on cage contacts was completely removed and medium / high cage contact wear observed. The results of these experiments are consistent with many previous observations for grease-lubricated Roller bearings tested under extreme conditions.

b. Behavior of PRCA-coated cages (Comparative)

2 shows the behavior of a PRCA-grafted polymer coating on cages. The compositions of these coatings were based on fluoro and acrylate polymers. It can be seen that high running temperature (> 50 ° C) and high temperature peaks were recorded for all bearings tested with PRCA coated cages. It is obvious that the very high running temperature, especially during the first few days, resulted from a thicker coating compared to the usual coating thickness. The high temperature spikes are due essentially to the lack of lubricant supply to the rolling / sliding contacts and to the fact that the coatings used could not suppress high frictional forces generated on contacts. The ratings of these bearings (Nos. 1, 3, 5 & 6) were unsatisfactory as shown in Table 4. Interestingly, bearing 1 showed no pronounced brown stripes on rolling elements, but circumferential wear scratches on rollers. The bearing contacts showed high wear on the coatings and slight to medium wear on the metal of the cage bar. Also, the PRCA coatings showed poor adhesion to the metal substrates, rendering them unsuitable for medium / high stress sliding applications.

c. Behavior of Eeonyx-coated cages

A number of attempts have been made to observe the behavior of Eeonyx polymer coating on SRB cages. 3 shows the running temperature of 5 bearings tested. Although few temperature peaks were observed in three runs, it can be seen that the overall running temperature is low compared to the standard phosphate coating or the PRCA coatings. The low running temperature requires solid lubricant between roller and cage contacts, and the observed temperature peak for the bearings tested is due to uneven quality of the coating process. Bearings # 7 and # 12 performed really well under experimental conditions.

table 4 shows the behavioral classification of this type of coating. On the No. 7 and 12 bearing elements did not show brown streaks. However, the other three bearings tested left some discolored stripes recognize on only one side of the bearing rollers. This observation agrees very well with the results of bearing temperature, such as discussed above. Bearings ranked 5 showed minimal cage wear and a easy wear on the steel of the cages is for the Lagerrangstufe 3 observed. It must be stated that the thickness of the applied coating is about 5 μm and it is anticipated that a slightly thicker coating would improve the behavior.

d. Behavior of others Anti-friction coatings

Commercially available coating methods based on PTFE / Mo ₂ S or MoS ₂ were also investigated. The 4A and 4B show the running temperature for 4 tested bearings. It can be seen that there is no unusual or rapid temperature rise and that the total recorded temperature was in the range of 40 ° C. This means that the mean running temperature is about 5-10 ° C lower than with the standard phosphate coating. The cages of the camp 16 were deliberately tested with a residual phosphate + MoS ₂ coating. The test result suggests that the storage behavior is not significantly affected, whether the cages were phosphated before the MoS ₂ coating or not. The A Stages of storage behavior of all bearings tested with these commercially available anti-friction coatings on cages were excellent as shown in Table 4. Minimal cage wear was observed for all bearings tested.

Table 4

e. Summary: Comparison between selected coated cages

5 shows a comparison between the bearing behavior of uncoated steel cages, phosphate cages, PTFE / MoS ₂ cages (Eeonyx, Dowty) and MoS ₂ - (Molykote 7409) coated cages. It can generally be concluded that the MoS _2- containing solid lubricant coatings behave better than the standard cages with or without phosphate coating. The results clearly suggest that a solid lubricant coating can improve bearing performance by inhibiting the formation of brown stripes on rollers and races.

5. Conclusions

Based on the above results, it can be concluded that the problem associated with the formation of brown stripes on rollers and races of grease-lubricated roller bearings is due to a solid lubricating coating to reduce running temperature, such as a PTFE / MoS ₂ or MoS ₂ (Molykote) coating on storage cages can be prevented. A 5-10 ° C lower running temperature is expected compared to manganese phosphate coated cages.

It Three methods were used to remove the chemicals on the metal surfaces of Apply running cages. The advantage of Eeonyx's method is that it's a quick one mechanical process is that it increases the coating thickness up Down to 3-5 μm and that it does not involve other chemical carriers. The commercial spray and dipping methods use and require other chemical binders a high temperature cure.

Claims (7)

A lubricated roller bearing, an outer and inner ring, rolling elements in the bearing space between the rings and a cage to hold the rolling elements at a predetermined mutual distance, wherein the cage is coated with a solid lubricant, characterized in that the solid lubricant coating a Disulfide and / or diselenide of a transition metal group V or VI. Lubricated rolling bearing according to claim 1, characterized in that the coating MoS ₂ and / or WS ₂ , preferably with an organic resin such as PTFE. Lubricated rolling bearing according to claim 1 or 2, characterized in that the coating applied by means of "shot blasting" on the cage becomes. Lubricated rolling bearing according to one the claims 1 to 3, characterized in that the thickness of the coating 5 to 12 μm is. Lubricated rolling bearing according to one the claims 1 to 4, characterized in that the bearing is a spherical roller bearing is. Method for reducing the running temperature of cages of lubricated rolling bearings to increase the Lifetime of lubricant in a lubricated rolling bearing and / or to increase the service life of a lubricated bearing, the lubricated roller bearing an outer and an inner ring, rolling elements in the bearing space between the rings and a cage around the rolling elements at a predetermined mutual distance, the method being characterized in that the bearing cage or the roller end with a solid lubricant coating according to a the claims 1 to 5 is coated. Use of solid lubricating coatings containing MoS ₂ and / or WS ₂ on lubricating bearing cages for reducing the running temperature of roller end flange contacts, rolling element cages and / or bearings, increasing the life of the lubricant in the bearing and / or increasing the useful life of a lubricated rolling bearing.